1. Field of the Invention
The present invention relates to an image reading apparatus for optically reading a document image and an image forming apparatus provided with such an image reading apparatus such as a copier, a facsimile machine or a complex machine of these.
2. Description of the Related Art
Generally, an image forming apparatus such as a copier optically reads a document image using an image reading apparatus and prints a sheet-like recording material such as a copier sheet based on read image data or transmits the read image data to a receiving-side facsimile machine via a communication tool.
The image reading apparatus irradiates a document with light from a light source in a carriage which moves in a sub scanning direction orthogonal to a main scanning direction of a document placed on a transparent platen. A beam of light reflected by the document is introduced in a specified direction by a mirror accommodated in the carriage, then focused by a lens and incident on a CCD (image sensor) arranged at a focus position to be read as image data.
In such an image reading apparatus, the carriage is slid in the sub scanning direction along a round bar-like guide rail. Here, due to vibration, a variation of sliding resistance or the like produced upon moving the carriage, the carriage may possibly swing by as much as a fitting clearance with the guide rail. In this case, since a read image is distorted, it becomes difficult to accurately and stably read an image.
Conventionally, several techniques have been proposed to prevent or suppress such a swinging movement. However, these techniques are accompanied by complicated structures, causing a new problem of leading to a product cost escalation of the image reading apparatus.